JPS6358237B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for electrolytically removing an oxide film generated on the non-plated surface in the production of single-sided alloyed hot-dip galvanized steel sheets. In the manufacturing process of single-sided hot-dip galvanized steel sheets, the non-plated surface is easily exposed to the atmosphere due to the heating and cooling heat of the steel sheet, and the surface is exposed to FeO, Fe ₂ O ₃ ,
Many oxide films such as Fe ₃ O ₄ are generated. Therefore, in order to obtain a product with a clean surface on the non-plated surface, a step of removing the oxide film is required. The oxide film is oxidized due to repeated heat treatments during the manufacturing process of the galvanized steel sheet, and its adhesion is extremely strong. Therefore, it cannot be easily removed by ordinary pickling, etc., and is generally removed by electrolytic methods, chemical polishing methods, mechanical grinding methods, etc. Recently, importance has been placed on the weldability and paintability of galvanized steel sheets, and single-side alloyed hot-dip galvanized steel sheets, which are single-sided hot-dip galvanized steel sheets that are alloyed by further high-temperature treatment, have begun to be produced. Since this alloyed steel sheet has been subjected to high temperature treatment, the oxide film on the non-plated surface is more strongly adhered to than a normal single-sided plated steel sheet. Therefore, when applying an electrolytic method or a chemical polishing method to remove this oxide film, it is necessary to further improve the film removal performance by increasing the current density or the temperature of the processing solution. This inevitably improves the performance of eluting zinc plating, which causes a problem that adversely affects the quality of plating. In addition, when using a mechanical grinding method, since a larger grinding force is required, there is a problem that the quality of the non-plated surface is impaired, such as by creating linear surface flaws on the steel plate surface, and countermeasures have been desired. In response to the above-mentioned needs, the present invention aims to provide an excellent method for electrolytically removing the oxide film on the non-plated surface of a single-sided alloyed hot-dip galvanized steel sheet without impairing the plating quality of the steel sheet. In the present invention, when electrolytically removing an oxide film on the non-plated surface of a steel sheet coated with alloyed hot-dip galvanized steel sheet on one side, anodes are provided so as to face each other on both sides of the galvanized steel sheet in an electrolytic solution, and between the anodes. A method of removing the oxide film on the non-plated surface by passing the plated steel plate as a cathode, and a single-sided alloy in which an appropriate amount of an inhibitor is added to the electrolyte in the above method to more completely prevent zinc dissolution in the plated alloy. The gist of this article is a method for removing oxide film on the non-plated surface of hot-dip galvanized steel sheets. A conventional method for electrolytically removing an oxide film on the non-plated surface of a single-sided galvanized steel sheet includes, for example, as shown in the side view of FIG. There is an electrolytic removal method using a so-called pair of anodes, in which an anode 5 is provided in an electrolytic solution 3. If this method is used to remove the oxide film on the non-plated surface of a single-side alloyed galvanized steel sheet, there is a drawback that the oxide film on the non-plated surface is removed and the zinc plating on the plating surface 4 is also immersed, degrading the plating quality. The present inventors conducted various experimental studies to solve this problem, and attempted an experiment in which, in addition to the anode that faces the non-plated surface (cathode) of the conventional method described above, an anode that also corresponds to the plated surface on the opposite side was provided. Ta. In other words, by electrolysis using so-called two-pair anodes, in which anodes are placed opposite to each other on both sides of a cathode-plated steel sheet passing through an electrolytic solution, the film removal performance of the oxidized film on the non-plated surface is improved, and the electrolysis on the plated surface is improved. A new fact was discovered that the elution of zinc oxide is prevented by protecting it from the reaction. Furthermore, it was confirmed that the ability to protect the plated surface was further enhanced by adding an inhibitor to the electrolytic solution during electrolysis at the two counter anodes. This is because when two opposite anodes are provided, during electrolysis between the plated surface and the corresponding anode, the zinc contained in the electrolyte is first deposited on the plated surface to form a zinc film, and this zinc film forms a zinc film. It is thought that the plated surface is protected and the elution of the plated zinc is prevented, and the effect of preventing the plated zinc from elution is further enhanced by the inhibitor added to the electrolyte. The present invention will be explained in more detail below. FIG. 2 is a side view showing an example of the method of the present invention. 6 is a single-sided alloyed hot-dip galvanized steel sheet, 7 is an electrolytic cell, and 8 is an electrolytic solution. 9, 9 is an anode, liquid 8
The plated steel plates 6 are placed vertically in parallel at appropriate intervals, and the plated steel plates 6 are immersed in the liquid 8 by applying a voltage to the cathode with the upper surface as the non-plated surface 6 ₁ .
Thread the plate in the direction. 10 is conductor roll, 1
1 is a sinking roll, and 12 is a squeezing roll. FIG. 3 is a side view showing another example of the method of the present invention. In Figure 3, the anodes 9 and 9 in Figure 2 are arranged vertically in parallel, and a plated steel plate 6 is passed between the anodes 9 and 9 in the direction of arrow b to electrolytically remove the oxide film on the non-plated surface. It was designed to do so. The method of the present invention will be explained based on FIG. The single-side alloyed hot-dip galvanized steel sheet 6 that has undergone the alloying treatment is applied to a cathode by a conductor roll 10, guided into an electrolyte 8 by a sinking roll 11, and passed between anodes 9, 9. , an oxide film of FeO, Fe ₂ O ₃ , Fe ₃ O ₄ etc. attached to the non-plated surface 6 ₁ is electrolytically removed. A commonly used H ₂ SO ₄ solution is used as the electrolyte 8, and its concentration is preferably 3 to 15% H ₂ SO ₄ .
Furthermore, by adding an inhibitor that suppresses the elution of zinc to the electrolytic solution 8, the protective effect of the plating surface during the removal of the oxide film by electrolysis is further promoted, but the amount of this inhibitor added is 0.5
% or less is sufficient. In the above electrolysis, the temperature of the electrolytic solution is preferably 70° C. or higher, the current density is 20/dm ² or higher, and the treatment time is preferably 5 seconds or higher. Next, examples of the present invention will be described. Example 1 In a single-sided alloyed hot-dip galvanized steel sheet with a galvanized coating amount of 40 to 45 g/m ² on the plated surface, the composition was FeO−Fe ₃ O ₄ −Fe ₂ O ₃ attached to the non-plated surface,
An oxide film with a film thickness of 6 to 7 μm and a film weight of 30 to 36 g/ ^m2 ,
A test steel sheet was obtained by electrolytically removing the material using an electrolytic device with two opposite anodes 9, 9 shown in FIG. The electrolysis conditions in the above electrolysis are that the electrolyte composition is 6%
The electrolytic treatment time was 15 seconds using H ₂ SO ₄ and a liquid temperature of 70 to 75°C. As a comparative example, an oxide film on the non-plated surface of the same single-sided alloyed hot-dip galvanized steel sheet as above was applied under the same electrolytic conditions to the conventional one-pair anode 5 shown in FIG.
A test steel sheet was obtained by electrolytic removal using an electrolytic device. In the above two examples, the current density, the amount of oxide film (Fe) removed from the non-plated surface, and the amount of oxide film (Fe) removed from the plated surface are
Table 1 shows the measurement results of the amount of Zn eluted.

[Table] As shown in Table 1, when using the conventional method, the Fe removal rate was 100% at a current density of 40 A/dm ² , and the oxide film on the non-plated surface was completely removed, but at the same time, the oxide film on the non-plated surface was completely removed. The Zn volume was 6.3 to 7.0 g/ ^m2 , and a large amount of Zn was eluted from the plating surface, and the plating surface also became black and sooty, deteriorating the plating quality. On the other hand, in the case of the method of the present invention, the current density is 20A/dm ²
The Fe removal rate was 100%, and the oxide film on the non-plated surface was completely removed, and the amount of Zn leached from the plated surface was suppressed to only 0.3 to 0.4 g/ ^m2 , and there was no effect on the plated surface. The purpose of preventing zinc elution from the plating surface was achieved. Example 2 In a single-sided alloyed hot-dip galvanized steel sheet with a coating weight of 40 to 45 g/m ² on the galvanized surface, galvanization adhered to the non-plated surface. The composition is FeO−Fe ₃ O ₄ −Fe ₂ O ₃ ,
An oxide film with a film thickness of 6 to 7 μm and a film weight of 30 to 36 g/ ^m2 ,
Using an electrolytic device with two opposite anodes 9, 9 shown in FIG. 2, and adding an inhibitor to the electrolyte,
It was electrolytically removed and used as a test steel sheet. The electrolytic conditions for the above electrolysis are as follows: 6% H ₂ SO ₄ : solution is used as the electrolytic solution, 0.5% of Super Raviclean SR-501 (trade name) is added as an inhibitor, and the solution temperature is
The temperature was 70 to 75°C and the electrolytic treatment time was 15 seconds. In addition, as a comparative example, an oxide film on the non-plated surface of a single-sided alloyed hot-dip galvanized steel sheet similar to that described above was prepared using the conventional electrolytic device with one counter electrode anode 5 shown in FIG.
A test steel sheet was obtained by electrolytically removing the electrolytic solution under the same electrolyte composition, solution temperature, and electrolytic treatment time as described above without adding an inhibitor. In the above two examples, the current density and the removal rate of the oxide film (Fe) on the unplated surface and the plated surface
Table 2 shows the measurement results of the amount of Zn eluted.

[Table] As shown in Table 2, when using the conventional method, the amount of Fe removed was 100% at a current density of 40 A/dm ² , meaning that the oxide film on the non-plated surface was completely removed, but at the same time, the oxide film on the non-plated surface was completely removed. The amount of Zn eluted from the plating surface was 6.3 to 7.0 g/m ² , and a large amount of Zn was eluted from the plating surface, and the plating surface also turned black and sooted, deteriorating the plating quality. On the other hand, in the case of the method of the present invention, the Fe removal rate was 100% at a current density of 20 A/dm ² , and the oxide film on the non-plated surface was completely removed, and the amount of Zn eluted from the plated surface was 0.1 to 0.2. g/m ² as shown in Table 1, the suppression effect was further improved, and the purpose of preventing zinc elution from the plating surface was completely achieved. As described above, when electrolytically removing an oxide film on the non-plated surface of a single-sided alloyed galvanized steel sheet, the present invention provides an anode opposite to both sides of the galvanized steel sheet, or provides an anode on both sides and an inhibitor in the electrolyte. It has become possible to easily and effectively electrolytically remove the oxide film on the non-plated surface without almost completely impairing the plating quality by adding a single-sided alloyed hot-dip galvanized steel sheet. It is extremely effective in improving quality and reducing costs.

[Brief explanation of drawings]

FIG. 1 is an explanatory view of a conventional method for electrolytically removing an oxide film on the non-plated surface of a single-sided hot-dip galvanized steel sheet, and shows a longitudinal side view. FIGS. 2 and 3 are explanatory diagrams of an example of the method of the present invention, showing a longitudinal side view. 1, 6: single-sided plated steel plate, 2, 6 ₁ : non-plated surface, 3, 8: electrolyte, 4: plated surface, 5, 9: anode, 7: electrolytic bath, 10: conductor roll, 1
1: Sinking roll, 12: Squeezing roll.

Claims (1)

[Scope of Claims] 1. When electrolytically removing an oxide film on the non-metallic surface of a steel sheet that has been subjected to alloyed hot-dip galvanizing on one side, anodes are provided in an electrolytic solution so as to face each other on both sides of the galvanized steel sheet, A method for removing an oxide film on a non-plated surface of a single-sided alloyed hot-dip galvanized steel sheet, which comprises passing the plated steel sheet as a cathode between the anodes to electrolytically remove the oxide film on the non-plated surface. 2. When electrolytically removing the oxide film on the non-plated surface of a steel sheet that has been subjected to alloyed hot-dip galvanizing on one side, an inhibitor is added to the electrolytic solution, and an inhibitor is added to the electrolytic solution so that it faces both sides of the galvanized steel sheet, respectively. A method for removing an oxide film on a non-plated surface of a single-sided alloyed hot-dip galvanized steel sheet, comprising: providing an anode, and passing the plated steel sheet as a cathode between the anodes to electrolytically remove the oxide film on the non-plated surface.